Various types of closures have been devised, and many closures vary considerably in design depending upon the size of the closure and the pressure rating to which the closure is subjected. Closures are desirably fast opening and closing, and provide a reliable seal to maintain pressure within the vessel. Most closures are of the type wherein the door is threaded or otherwise mechanically secured to a hub, and is sealed to hold pressure. The internal pressure acts to push the door away from the hub, which may reduce sealing effectiveness.
A rather complicated closure mechanism is disclosed in U.S. Pat. No. 6,439,415. U.S. Pat. No. 5,148,938 discloses an exterior stop, and a simple interference seal between the interior of the housing and the exterior of the door. U.S. Pat. No. 4,519,519 discloses a door with a stop exterior of the door, and a seal between the interior of the door and the body of the vessel. U.S. Pat. No. 2,721,094 discloses keys which move radially to lock the door in place or release the door. U.S. Pat. Nos. 7,051,897 and 7,036,674 disclose other embodiments of closures for a pressure vessel. Prior art closures of this type are generally expensive, and these closures frequently have detractions which have limited their use and acceptance.
Various closures have been designed which utilize a door interior of a stop on the hub. This design thus utilizes internal pressure to press the door tighter against a stop. U.S. Pat. No. 3,667,649 discloses a design wherein the stops are removable. U.S. Pat. No. 3,449,860 discloses a door with retractable stops. U.S. Pat. No. 4,140,240 discloses a closure with stops external to the door.
The disadvantages of the prior art are overcome by the present invention, and an improved closure is hereinafter disclosed. These and further features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.